Who, What, Why: How do flying ants know it's mating day?

It's time for flying ant day in large parts of the UK, when they embark on their annual mating ritual. So how do the ants know it's their one day a year to mate?

The sun has finally come out, summer has arrived and with it comes the annual swarm of flying ants.

This seasonal appearance occurs when the ants embark on their "nuptial" flight. This mating ritual happens on roughly the same day across the country, with some regions following a day or two afterwards.

For the ants it is the first step in founding new colonies. So how do they know which day it will happen?

Scientists don't fully understand how the ritual works but do know weather is important. Ants pick a day by sensing temperature, humidity and day length, says Dr Mark Downs, of the Society of Biology. Warm, humid conditions are perfect. Heat makes it easier for them to fly and humidity makes the ground softer for mated queens to dig nests. How flights are synchronised between nests is still not fully understood, some suggest once ants begin to fly they give off a chemical smell that others detect.

"Ants are not the strongest fliers and they mate on the wing, so their chances of mating are greatly reduced if they come out in the rain," says Downs. "Humidity and wet weather prior to the flight also means that the ground is soft, which makes it easier for the queens to burrow down and make a nest once they have mated.

"Given there's been a lot of rain over the last few weeks and now there's heat, it looks likely that most will come out over the next day or so."

Flights are synchronised between nests because the flying ants need to maximise their chances of meeting ants from other colonies to mate with. Downs says scientists still don't fully understand how this "extraordinary" synchronisation happens, with more research being done.

Queens mate with males during flight, after which the female will lose her wings and attempt to start her own colony by burrowing into the soil. Males die shortly after mating but queens can live for up to 15 years.

"The queens themselves, once they have gone down to burrow, will not eat for six to eight weeks," says Downs. "They will live off the vestige of their wings for energy while they raise their first larvae."

The most common flying ant seen at the moment is the black garden ant, the Lasius niger. The ants seen throughout the year are workers.

The Society of Biology is studying the emergence pattern of mating ants across the UK. It is asking member of the public who see flying ants to make a note of the time, date, location and weather conditions. The details can be submitted online though its website.

"We want to find out just how synchronised the emergence of flying ants is across the UK," says Down.

Biologists from the University of Girona recently published a study based on data from "nuptial" flights of the seed-harvester ant, which may help understand the flights of UK species.

The data was gathered over a six-year period last year on the Iberian peninsula and the scientists were able to identify clusters of "nuptial" flight that appeared to be triggered by the same weather fronts.

The study found the days with the highest number of flights consistently occurred a couple of days or so after rain had stopped and was clear of the peninsula.

Ants play an important role in the ecosystem, among other things they improve soil quality, help pollinate flowers and feed on pests. They are also an important source of food for other animals.